Crane interlock mechanism



V. T. PILIPCZUK CRANE INTERLOCK MECHANISM Jan. 26, 1960 2 Sheets-Sheet 1Filed July 18, 1957 ki?, Il@

Jan. 26, 1960 v. T. PILlPczUK CRANE INTERLOCK MECHANISM 2 Sheets-Sheet 2Filed July 18, 1957 may XQM.

United CRANE INTERLOCK MECHANISM Vincent T. Pilipczuk, Norwood Park,Ill., assignor to Borg-Warner Corporation, Chicago, Ill., a corporationof Illinois Application July 18, 1957, Serial No. 672,726

9 Claims. (Cl. 104--98) The invention relates to material handlingdevices of the type comprising a pair of relatively movable tracks orbeams having a carriage movable on the tracks; and, more particularly,the invention relates to cranes of the type comprising a transversegirder or beam supported at opposite ends thereof by trolley wheelsadapted to roll along overhead tracks. Still more particularly, theinvention relates to mechanisms for interlocking the movable girder witha stationary beam to provide for the transfer of a carriage movablydisposed on the transverse girder onto the stationary beam.

It is an object of the invention to provide an improved interlockmechanism of this type having an assembly on one of the beams comprisinga plunger projectable to interlock with an assembly on the other beamand with interconnecting means being provided on the two assemblies sothat the plunger is prevented from projecting movement until there issubstantial alignment between the two beams.

It is another object of the invention to arrange the interlockingmechanism such that it can be controlled both in locking the two beamstogether, or in unlocking them, by means of a single control handle orlever.

It is also an object of the invention to provide stop arms on each ofthe assemblies on the two beams for preventing accidental movement ofthe carriage off either of the beams when they are not in alignment andto provide gearing for actuating the stop arms to raise them out ofcarriage blocking position after the plunger has been projected from oneof the assemblies into the other. More particularly, it is an object tomake the plunger in the form of a rack by means of which it can be movedby the actuating lever or handle and which may cooperate with spurgearing for actuating at least one of the stop arms.

It is another object of the invention to provide a ratchet mechanism forpreventing a return of the stop arms and the plunger until they havemade complete movements to unblocking and interlocking positionsrespectively, so that once the interlocking action of the interlockmechanism has begun, the interlocking action must be completed. In thisconnection, it is also an object to provide releasable means for theratchet mechanism, so that the actuating handle may -be moved to thelimit of its movement for the purpose of unlocking the interlockingmechanism so that all of its parts m-ay return to their originalpositions with the stop arms thereafter blocking movement of the movablecarriage and with the plunger being completely retracted from theassembly with which it mates.

The invention consists of the novel constructions, arrangements anddevices to be hereinafter described and claimed, for carrying out theabove stated objects, and such other objects as will be apparent fromthe following description of a preferred form of the invention,illustrated with reference to the accompanying drawings, wherein:

Fig. 1 is' a side elevational view of a movable crane ICC 2 togetherwith a stationary beam with which the interlocking mechanism of theinvention may be used, for the purpose of interlocking the crane andbeam together to allow the transfer of a movable carriage from one tothe other;

Fig. 2 is a top plan view of the interlock mechanism of the invention;

Fig. 3 is a sectional view taken on line 3 3 of Fig. 2;

Fig. 4 is a sectional View taken on line 4-4 of Fig. 2; and

Fig. 5 is a view taken from line 5--5 of Fig. 3.

Like characters of reference designate like parts in the several views.

The interlock mechanism of the invention may be used in connection withthe underhung, single girder crane illustrated in the drawing. The cranecomprises a single horizontally extending I-beam girder 10 having upperand lower flanges 11 and 12. A pair of end trucks 13 and 14 are xed tothe girder 10. Each of the trucks 13 and 14 comprises a pair of spacedangle bars 15 and 16 fixed to the top flange 11 of the girder 10. A pairof tread-wheels 17 are rotatably fixed with respect to the angle bar 15,and a pair of treadwheels 18 are rotatably fixed with respect to theangle bar 16.

The end truck 13 is suspended from a depending I-beam track 19, and theend truck 14 is suspended from a depending I-beam track 20. Each of theI-beams 19 and 20 is fixed to any suitable support such as to a ceiling21. Each of the beams 19 and 20 has a lower ilange 22, and the wheels 17for each of the trucks 13 and 14 are positioned on one side of theflange 22 of one of the I-beams 19 and 20, and the Wheels 18 arepositioned on the other side of the angc 22 of this -beam so that thewheels 17 and 1S roll on the anges A load supporting trolley or carriage23 is movably disposed on the girder 1i). The carriage 23 comprises twoend plates 24 disposed on opposite sides of the girder 10, and each endplate carries a pair of treadwheels 25 and 26. The treadwheels carriedby one of the end plates 24 rest on one side of the lower flange 12, andthe treadwheels carried by the other end plate 24 rest on the other sideof the tlange 12'. A yoke 27 connects the two end plates 24 together,and a hook 28 is xed vitldi respect to the yoke 27 for supporting anysuitable The carriage 23 may be moved longitudinally with respect to thegirder'lt) by simply applying force in one direction or the other to thecarriage, so that the wheels 25 and 26 roll on the upper surfaces of theange 12, and the girder 10 may be moved longitudinally with respect tothe I-beam tracks 19 and 20 by also applying a force in one direction orthe other to the girder 10 causing the wheels 17 and 18 to roll on theupper surfaces of the anges 22.

The girder 10 which is movable on the I-beams 19 and 20 as justdescribed may be aligned with an I-bearn girder 29 which is xed to theceiling 21. The I-beam 29 has upper and lower flanges 30 and 31, and theI-beam 29 is xed with respect to the ceiling 21 by means of a pair ofspaced I-beams 32 and 33 fastened to the ceiling 21 and the flange 30.When the girder 10 isso positioned along the I-beam tracks 19 and 20that the girder 10 is in alignment with the I-beam 29, the carriage 23may be rolled onto the I-beam 29 from the girder 10, and the device ofthe present invention is provided on the girder 10 and I-beam 29 for thepurpose of mechanically aligning the I-beams 10 and 29 and holding themin alignment and for preventing movement of the carriage 23 off eitherof the I-beams 10 and 29 until such alignment has been obtained.

The crane interlock mechanism comprises two assemblies, namely, aplunger projecting assembly 34 and a plunger' receiving assembly 35mounted on adjacent ends of the l-bearns l and 29. The Iassembly 34comprises a baise plate 36 fixed on the top flange 11 of the girder andtwo side plates 37 and 38 fixed to the base plate 36. A plunger in theform of a rack 39 is slidably disposed between the side plates37 and 38on the upper surface of the base plate 36 and has teeth 40 on its upperface which are in mesh with the teeth 41 of a gear 42. The gear 42 isfixed on a shaft 43 which extends through the plates 37 and38. yAnactuating lever 44 is fixed on one end'of the shaft 43, and a ropehandle 45 is provided at the free end of the lever 44. A collar 46 isfixed on the shaft 43, and a lever return spring 47 is disposed aboutthe shaft 43 and has one end 48 fixed in the collar 46 and has its otherend 49 extending into the side plate 38 to be fixed with respectthereto.

A gear 50 having teeth 51 fixed on a shaft 52 extending through the sideplates 37 and 38 is adapted to mesh with lthe gear 42.V The rack 39 has.some of its teeth 4G ground away for a part of their length to provide afiat surface'i53 on the top of the rack 39 so as to provide clearancewith respect to the gear 50, and the gear 42 Ahas some .of its teemitlground away for a portion of their'length'to provide a smooth outercylindrical surface S4 on a portion of its periphery foreclearing thegear 50 for a certain degree of rotation of the gear 42. i

A ratchet wheel 55 having ratchet teeth 56 on its periphery is fixed onthe shaft 52 on one side of the gear `50 betweenthe lside plates 37 and38. A pair of stop arms S7 and 58 are fixed on opposite ends of theshaft 52. The stop arms 57 and 58 extend downwardly closely adjacent theedges of the upper liange 11 and are limited in their movement byoutwardlyprojecting lug portions 59 and 68 formed on the base plate 36.A washer 61 is disposed between the side plate 37 and the arm 53, and acam 62 is disposed between the arm 57 and the other side plate 38. Thecam 62 is provided with a notch 63 on its periphery and has a lostmotion connection with the shaft 52 comprising a slot 64 formed withinthe cam 62 and a key 65 fixed in the shaft 52 and movable in the slot64.

A pawl 66 is swingably mounted on a stud 67 extending etween the sideplates 37 and 38. A spring 68 is disposed about the `stud 67 and isfixed in the side plate 37 at one end and lis looped about the pawl 66at its other end so as to yieldably hold the pawl 66 in engagement withthe ratchet wheel 55. A pin 69 is fixed in the pawl 66 and extendsthrough a hole in the side plate 38 so that the cam 62 when rotated maycontact and act on the pin 69.

A pawl 70 is Vswingably disposed on a stud '71 extending through theside plate 37 and 38. The pawl 7l)` is held centralized with respect tothe side plates 37 and 38 by collar portions 72 and is provided with arounded end 73 adapted to fit between adjacent teeth 41 and with alaterally extending end portion 74 by means of which the pawl 70 may beswung as will be hereinafter described. A pin 75 also extends betweenthe plates 37 and 38 for limiting movement of the rack 39, and a stud 76is also provided between the side plates 37 and 33 for assisting' thestuds 7l and 67 in holding the plates 37 and 38 properly spaced withrespect to each other.

The assembly 35 comprises a base plate 77 fixed on the upper flange 30of the I-beam 9.9 on the end of the I-beam andtwo side plates 78 and 79fixed to the base plate. A gear 80 having teeth 81 is fixed on a shaftS2 extending through the side plates 78 and 79. Two stop arms 83 and 84similar to the stop arms 57 and 58 are fixed on the shaft S2 and areheld properly spaced with respect to the side platesV 78 and 79 bywashers-61, so that the side arms clear the edges of thetiange 30 by .4only a slight margin. The base plate 77 is provided with outwardlyextending lug portions 85 and 86 for limiting rotative movement of thearrns 83 and 84.

A pair of bearings 87 and 88 are fixed on the base plate 77 by means ofstuds 89, and the bearings 37 and 88 are so spaced that the raclf; 39may pass between them. The end of the rack 39 is tapered to facilitateits entrance between the bearings 87 and 88, as shown.

A cam 90 is disposed in recesses in the forward edges of the side plates-78 and 79 and is held fixed by a stud 9i extending between the sideplates 78 and 79. The cam 90 is provided with arelatively high edge 92and with slanted top edges 93. yA stud 94 irl-addition to the stud 91functions to hold the plates 78 and 79 properly e are aligned with eachother.

spaced.

It will be apparent that the assembly 34 is fixed on the upper surfaceof the I-beam 10 adjacent its end and the assembly 35 ,is fixed on theadjacent end of the I-beatn l29; vand there is only a slight clearance,such as, for example,approx;irnately a quarter inch, between the plates37 and 3,8 of the assembly 34 and the plates 78 and 79 of the assembly35 when the I-beams 1d and 29 The arms 57 and S8 and the arms 83vand 84are respectively closely spaced to the edges of the flanges 11 and 30,and these arms are in the path of movement of the arriage 23 when thearms 57, 5.8, 83 and rS4 extend vertically downwardly.

In operation, when it is desired to transfer the carriage 23, togetherwith any load held suspended by the hook 28, from the crane to the fixedI-beam 29, the girder 10 -is moved longitudinally of the I-beam tracks19 and 2f) with the rollers 17 and 1 ;8 of the end trucks 13 and i4rolling on the, lower flanges 22 of the l-beams 19 and 2 0 until thegirder 41() is in substantial alignment with the I-beam 29. Brior tosuch alignment, the parts of the assembly 34 are in their positions asillustrated, and the arms-57, 58, .33 and v84- extend verticallydownwardly in abutting contact with the stops 59, `60, and 86,respectively. The arms 57, 58, 83 and 84 are only slightly spaced fromthe sides of the upper anges l1 and 30, and the arms 57 and 58effectively block movement ofthe carriage 23 off the end of the girder10. If, prior to such alignment of the beams 10 and 29, the lever 44 hasmanual force applied to it from the handle 45 tending to turn the shaft43 in the counterclockwise direction as seen in Fig. 3, the pawl 70 andparticularly its rounded end 73 prevents such movement 0f the shaft 43since the rounded pawl end 73 fits between teeth 41 of the gear 42 fixedon the shaft 43.

As the girder 10 is moved into alignment with the l-beam 29, the leverend 74 of the pawl 76 moves over o'ne of the slanted top edges 93 of thecam 90 and onto the high part 92 ofthe cam 90. The pawl 7l) is thusrotated about the stud 71 so that the rounded end '73 is moved out ofengagement with teeth `41 of the gear 42, and the gear 42 is then freeto rotate in the counterclockwise direction. Under these conditions,when the lever 44 is rotated by manual effort applied to the handle 45,the gear 42 due to its meshing relationship with the plungeror rack 39.,vmoves the plunger 39 outwardly to the right as seen in Fig. 3, so thatthe plunger 39 passes between the; bearings 87 and 88 of the assemblyThe. end of the plunger 39` is tapered., and it may contact and rideover one, or the other of the bearings 87 and S8 and cam the beams 10and 29V into substantially perfect alignment, kassuming the beams areinitially slightly misaligned when the plunger 39 is projected.

Due tothe cut out portio'n 53 provided on the rack 39, this movement ofthe. rack of itself has no effect on the gear 5.0,. and dueto the cutout portion 54 of the gear 42, Ainitial movement of the gear 42 likewisehas no effect on the gear 5f). Continued movement of the lever 44,causes additional rotation of the gear 42 fixed on the shaft 43 andmoves the rack` 39 completely between the. rollers: 8.7; and` 88.7 so.asto. effectively fix. the girder 10 against movement relative -to theassembly 35 and the fixed beam 29. It will be apparent that suchmovement of these parts is against the action of the spring 47encircling the shaft 43.

After a predetermined movement of the lever 44 and gear 42, the teeth 41at the end of the cut out portion 54 on the gear 42 begin to mesh withthe teeth 51 on the gear 50, and continued rotation of the gear 42 bythe lever 44, which is in the counterclockwise direction as seen in Fig.3, causes a rotation of the gear 51 in the opposite direction. The stoparms 57 and 58 are fixed on the shaft 52 which is, in turn, fixed withinthe gear 51, and the stop arms 57 and 58 are thus swung upwardly out ofthe path of movement of the carriage 23.' At the same time that theteeth 41 of the gear 42 begin to intermesh with the teeth 51 of the gear50 to begin the swinging movement of the stop arms 57 and 58, the endtooth 40 on the rack 39 intermeshes between teeth 81 of the gear 80, andthe continued rotation of the gear 42 that causes the arms 57 and 58 tobe moved out of the path of movement of the carriage 23 likewise causesa corresponding movement of the stop arms 83 and 84 through theintermeshing rack 39 and the gear 80. When the stop arms 57, 58, 83 and84 are all out of the path of movement of the `carriage 23, the carriage23 can be moved from the girder 10 onto the stationary I-beam 29 withthe rollers 25 and 26 rolling over the upper surfaces of Ithe iiange l2of the girder 10 onto the upper surfaces o'f the flange 31 of the I-beam29. During this movement of the carriage 23, therack 39 projectedbetween the bearings 87 and 88 locks the girder 10 and I-beam 29 inalignment.

The ratchet wheel 55 is xed on the shaft 52 along with the gear Si), andthe pawl 66 ratchets over the ratchet teeth 56 as the arms 57 and 58rotate upwardly out of stopping relationship with respect to theycarriage 23. The pawl 66 as it engages diierent ones of the ratchetteeth 56 prevents a return movement of the gear 50 in thecounterclockwise direction until the lever 44 has been swung mo're thansuflciently to move the arms 57 and 58 (and also the arms 83 and 84which move with the arms 57 and 58 due to the gears 50 and 80 and therack 39 interconnecting them) to cornpletely clear the carriage 23. Thusthe lever 44 may be swung sufciently to causesuicient swinging movementof the arms 57, 58, 83 and 84 to allow the carriage 23 to be moved fromthe girder 10 to the I-beam 29, and the pawl 66 co-acting with theratchet wheel 55 prevents a return movement of the arms 57, 58, 83 and84 even though the handle 45 is released by the operator.

When the `transfer of the carriage 23 from the girder 10 to the I-beam29 has been completed, the lever 44 is pulled still farther downwardlyto rotate the shafts 43 and 52 and gears `4-2 and 50 an additionalamount. The cam 62 has a lost motion connection with the shaft 52, andthe cam 62 turns along with the shaft 52. Upon this additional rotationof the gear 50 and shaft 52, the cam 62 -acts through the pin 69 on thepawl 66 and moves the pawl `66 yagainst the yaction of the spring 68 outof mesh with the ratchet wheel 5'5. At this time, the pin 69 has movedwithin the notch 63 of the pawl 62. Under these conditions, when thehandle 45 is released by the operator, the spring 47 returns the lever44 and thus the rack 39, the gears 42, 50 and Si) and the stop arms 57,58, 83 and 84 to their original positions, and during Ithese returnmovements of the parts until they reach their original positions, thepin 69 on the pawl 66 remains in the notch 63 of the cam 62 so that thepawl 66 is held out of engagement with the ratchet wheel 55 yand thepawl 66 does not prevent these return movements. When the parts areclose to their original positions, the key 65 abuts one end of the notch64 and moves the cam 62 in a counterclockwise direction as seen in Fig.4 so that the pin 69 moves out of the notch 63 and the pawl 66 returnsto its original position under the action of the spring 68, preventingyet light in weight.

counterclockwise rotation of the shaft 52 and-gear 50. With the carriage23 on the I-beam 29, the stop arms 83 and 84 prevent movement of thecarriage 23 olf the I-beam 29 until Ithe girder 10 is again aligned withthe I-beam 29 and the rack 39 is again projected between the bearings 87yand 88 to interconnect the assemblies 34 and 3S as has been described.When the I-beams yl0 and 29 are out of alignment and the arms 57, 58,`83 and 84 extend vertically downwardly, it will be apparent that thestop portions 59, 60, and 86 respectively cooperate with these arms tostop the movement thereof so that the arms positively prevent movementof the' carriage 23 off either of the I-beams 10 and 29 depending onwhich of these I-beams the carriage ispositioned.

The interlock mechanism advantageously is strong but The interlockmechanism is oper-ated by the single lever arm 44, and the craneoperator may thus have use of at least one hand forl other purposes. Thepawl 66 operating in conjunction with the ratchet Wheel 5S holds thestop arms 57, 58, y83 and 84- in upraised position, even though theoperator may completely release the handle 45, and the operator mayythus be completely free at this time to move the carriage 23 or toshift the load on -the hook 28, etc. A complete release of the arms 57,58, 83 and 84 back to Itheir original positions is obtained simply by anadditional pull on the handle 45. The interlock mechanism does not haveany protrusion, such as actuating fingers, that can be broken olf byincorrect usage of the interlock mechanism. -In this connection, thepawl 70 is actuated by the high portion 92 of the cam 90, and until thepawl 70 is completely actuated, any movement at allof the lever 44 bymeans of the handle 45 is prevented due to the action of the pawlportion 73 co-acting with .the gear 42.

I Wish it to be understood that the invention is not to be limited tothe speciic constructions and arrangements shown and described, exceptonly insofar as the claims may be so limited, as it will be apparent tothose skilled in the art that changes may be made without departing fromthe principles of the invention. In particular, I wish it to beunderstood that although I have referred to andk described a crane inconnection with my improved interlock mechanism, the interlock mechanismcan be used in connection with other material handling devices using apair of relatively movable tracks with a carriage adapted to move `onthe tracks, such as, so-called monorail systems, etc.

I claim:

1. In interlock mechanism, a pair of relatively movable tracks adaptedto carry a trolley movable thereon, a plunger projectably mounted on afirst one of said tracks, abutment means carried by the second one ofsaid tracks and adapted to co-act with said plunger for holding saidtracks in alignment for ythe transfer of the trolley from one track tothe other, a rack gear formed on said plunger, a drive gear rotatablycarried by said first track and meshing with said track for moving saidplunger to co-aot with said abutment means, a movable pawl lockable withthe teeth on rone of said gears for preventing projection of saidplunger, and a cam carried by said second track and moving said pawl outof locking position when said tracks yare moved into alignment tothereafter allow projection of said pawl. i

2. In interlock mechanism, a' pair of relatively movable tracks adaptedto carry -a trolley movable thereon, a trolley stop arm rotatablycarried 'by ya iirst one of said tracks and rotatable about a horizontal`axis transverse of said rst track from a position blocking movement ofthe trolley to a position permitting such movement, rst means mounted onsaid first one of said tracks including a movable lock element forholding said stop arm in its trolley blocking position, and a secondmeans including a cam carried by the second one Aofsaid tracks, saidlock element being actuated by said cam when said tracks are aeaassamoved into alignment 'to render the lock lelement ineiective. l

3. In interlock mechanism, a pair of relatively movable tracks adaptedvto carrya trolley movable thereon, a plunger projectably mounted onatirst one of lsaid tracks, abutment means carried by the second one -ofsaid tracks and adapted to co-act with said plunger "for 'holding saidtracks in alignment for thetransfer of the trolley from one track to theother, a trolley stop arm carried by each of said tracks and movablefrom a trolley blocking position to a position permitting movement ofthe trolley olf the end of the track, gearing interconnecting saidplunger and said stop arms for retracting said stop arms to permitmovement of said trolley from one of said tracks onto the other whensaid plunger is projected, a locking pawl carried by one of said tracksfor immobilizing said gearing and preventing projection of said plungerwhen said tracks are not in alignment, and a cam carried by the other ofsaid tracks adapted to actuate said pawl when said tracks are broughtinto alignment to release and mobilize said gearing.

4. In interlock mechanism, a track adapted to carry a trolley movablethereon, a trolley stop arm rotatably carried by said track and movablefrom a position blocking movement of the trolley along the track to aposition permitting such movement, a one way engaging mechanismengageable with said trolley stop arm for allowing movement of said stoparm from its blocking position to its unblocking position but preventingmovement in the opposite direction, and means for rendering said one waymechanism ineffective so that said stop arm may be returned from itsposition allowing movement of the trolley to its trolley blockingposition.

5. In interlock mechanism, a track adapted to carry a trolley movablethereon, a stop arm rotatably carried by said track and movable from arst position blocking movement of said trolley to a second positionpermitting such movement, a one Way engaging mechanism connected withsaid stop arm for permitting movement of said stop arm from its trolleyblocking position to its said second position but preventing movement ofthe stop arm in the opposite direction, and means energized by movementof said stop arm beyond its said second position for rendering said oneWay engaging mechanism inoperative so that said stop arm can return toits trolley blocking position.

6. In interlock mechanism, a pair of relatively movable tracks adaptedto carry a trolley movable thereon, a plunger projectably mounted on aiirst one of said tracks, abutment means carried by the second one ofsaid tracks and adapted to co-act with said plunger for holding saidtracks in alignment for the transfer of the trolley from one track tothe other, a pair of trolley stop arms each rotatably carried by one ofsaid tracks and each movable from a first trolley blocking positionpreventing movement of the trolley E the end of the track to a secondposition permitting such movement, rack teeth carried by said plunger,gearing interconnecting sair rack teeth and said stop arms so that saidstop aims are rotated by movement of said plunger after said plunger hascoacted with said abutment means for holding the tracks aligned, aratchet and pawl device eiective on said gearing for holding said stoparms from movement back to their trolley blocking positions after theyare rotated from such positions, and means rendered effective bymovement of said stop arms beyond their said second positions forrendering said pawl ineiective with respect to said ratchet allowingreturn of said stop arms to their trolley blocking positions.

7. In interlock mechanism, a pair of relatively movable tracks adaptedto carry a trolley movable thereon, a plunger projectably mounted on afirst one of said tracks, abutment means carried by the second one ofsaid tracks and adapted to co-act with said plunger for holding saidtracks in alignment for the transfer of the trolley from one track tothe other, a rack carried by said plunger, a pair of trolley stop armseach carried by one of said tracks and movable from a lirst positionblocking trolley travel oft' the end of the track to a second positionpermitting such travel, a driving gear in mesh with said rack, a handleconnected with said driving gear for rotating the gear so as to projectsaid plunger, a spring yieldably returning said driving gear and plungerto their original positions, a gear carried by said stop arm on saidsecond trackand co-acting with said rack for rotating said last namedstop arm out of its trolley blocking position on continued movement ofsaid plunger with respect to said abutment means, a gear adapted to meshwith said driving gear and connected with said trolley stop arm on saidfirst track so that said last named trolley stop arm is rotated out oftrolley blocking position along with the other of said stop arms, a pawland ratchet mechanism eiective on one of said stop arms for holding thestop arms from movement back to their trolley blocking positions oncethey are moved out of these positions, and a cam movable with said lastnamed stop arm for moving said pawl out of engagement with said ratchetto permit a returning movement of said stop arms towards their originaltrolley blocking positions, said cam having a lost motion connectionwithrespect to said last named stop arm so that said pawl is held out ofengagement with said ratchet to permit the complete return of said stoparms to their original positions before said pawl is reengaged with saidratchet.

8. In interlock mechanism, a track adapted to carry a trolley movablethereon, a trolley stop arm rotatably carried by said track androtatable about a horizontal axis transverse to said track and movablefrom a depending yposition blocking movement of the trolley along thetrack to an upraised position permitting such movement, a one-Wayengaging device engageable with said trolley stop arm for allowingmovement of said stop arm from its depending position to its upraisedposition and preventing movement from its upraised position toward itsdepending position, and means for rendering said oneway device inactiveso that said stop arm may be returned from its upraised position to itsdepending position.

9. In interlock mechanism, a track adapted to carry a trolley movablethereon, a trolley stop rotatably carried by said track and movable froma trolley blocking position to a position permitting movement of thetrolley, a handle drivingly connected with said trolley stop for somoving the stop on movement of the handle from a rst to a secondposition, a one-Way engaging mechanism engageable with said trolley stopfor allowing movement of a said stop from its blocking position to itsunblocking position but preventing movement in the opposite direction,and means under the control of said handle for rendering said one-Waymechanism ineffective when the handle is moved to an overtravel positionbeyond said second position so that said stop may be returned to itstrolley blocking position from its other position.

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